Fiber-reinforced composite materials, in particular, carbon fiber-reinforced composite materials (hereinafter referred to as the CFRPs) using carbon fibers are effective in reducing the weight of structures, and their demand has been increasing in airplanes, automobiles, etc. in expectation of improvement in fuel efficiency due to reduction in weight. A CFRP is produced by laminating and integrating layers of a prepreg obtained by impregnating a fabric of carbon fibers or a material composed of unidirectionally oriented carbon fibers with a resin. In a CFRP panel or the like, a peripheral portion becomes a region having an unstable quality because of the production process. Therefore, a method is employed in which a member is fabricated so as to include such a region as an extra peripheral portion in advance, and after the resin is cured, the extra peripheral portion is cut off to obtain a product.
In such a case, a water-jet method and an end-mill method are known as the method for cutting the extra peripheral portion. While the latter method in which an end mill is used is advantageous in that large-scale equipment is not required, an existing processing machine can be used, and the extra peripheral portion can be cut off without preparing pilot holes, a short end-mill life is a problem.
In order to increase the end-mill life, an end mill coated with a high-hardness coating (e.g., a diamond coating) has been employed. Since a CFRP is a material for which burrs easily occur, even when the abrasion of the cutting edge is considered to be at a level that does not cause a problem in metal machining, burrs occur in CFRP machining, and the tool (end mill) is determined to have reached the end of its life at that moment. Therefore, even in an end mill coated with a high-hardness coating, the end mill life is short in CFRP machining.
Furthermore, CFRPs used for fuselages, wings, etc. of airplanes are large in size in many cases, and fixing of such large workpieces easily becomes unstable because fixing points are limited during machining. Therefore, so-called “work chatter” occurs during machining, which results in damage to tool edges. This also shortens the tool life, and the short tool life results in an increase in the processing costs.
In this regard, Patent Ref 1 described below discloses a rotary cutting tool in which, in order to suppress the occurrence of burrs in machining of a fiber-reinforced composite material, inserts are mounted on a top of a shank, the inserts including right-handed helical cutting edges and left-handed helical cutting edges, and the right-handed helical cutting edges and the left-handed helical cutting edges are disposed alternately in the circumferential direction.    [Patent Reference 1] Japanese Unexamined Patent Application Publication No. 61-142009